Then 17-month-old Lexie Jade Melendez drinks from a stainless steel sippy cup on an outing with parents Melissa and Omar Melendez, both 25, in Lathrop, Calif. Since learning of the chemical BPA, Melissa Melendez has stopped using baby bottles containing the chemical.

For the first time, a large, population-based study links a chemical in plastic baby bottles to heart disease and diabetes in humans.

Some scientists say the study — released today to coincide with a Food and Drug Administration meeting— shows that bisphenol A, or BPA, is too dangerous to allow in consumer products, especially those used by babies and pregnant women.

U.S. government regulators on Tuesday defended their assessment that BPA is safe.

"A margin of safety exists that is adequate to protect consumers, including infants and children, at the current levels of exposure," Laura Tarantino, a senior Food and Drug Administration scientist, told an expert panel that has been asked for a second opinion on the agency's assessment of BPA.

FDA officials said they are not dismissing such findings, and conceded that further research is needed. "We recognize the need to resolve the concerning questions that have been raised," said Tarantino. But the FDA is arguing that the studies with rats and mice it relied on for its assessment are more thorough than some of the human research that has raised doubts.

The FDA last month released a draft report concluding that BPA doesn't pose a risk at the levels to which people are exposed every day. That puts the agency at odds with the National Toxicology Program, which this month expressed "some concern" that BPA alters behavior, the brain and prostate gland in children, both before and after birth.

BPA, used in everything from polycarbonate plastic bottles to the linings of metal cans, is one of the highest production-volume chemicals in the world, with 2 million tons made every year and demand growing at up to 10% annually, according to the new paper. Scientists from the Centers for Disease Control and Prevention have detected it in the urine of 93% of Americans tested.

Although scientists have published hundreds of studies about BPA's health risks, most experiments have used animals or cells, with only a handful of small studies in people, says co-author David Melzer of the University of Exeter in England.

His study, however, shows that adults with the highest BPA levels were more than twice as likely to have diabetes or cardiovascular disease than those with the lowest. In the study of 1,455 Americans, published online today in the Journal of the American Medical Association, adults with the highest BPA levels were also more likely to have abnormal liver enzyme concentrations, which indicate stress on that organ.

"This is a big deal," says Frederick vom Saal, a University of Missouri professor scheduled to speak at the FDA meeting today. "This isn't a drug taken by a few thousand people. This is every person in the United States being at risk for really serious disease."

Melzer says some of his findings are surprising.

BPA has never before been linked to heart attacks, Melzer says. His study is also the first to associate high BPA levels with disease in adults. Previous research has focused on BPA's effects on fetuses and babies, because they are believed to be most vulnerable to outside hormones, Melzer says.

Industry groups say it would be premature for the FDA to restrict BPA based on one study.

"While this study raises interesting questions, it provides no scientifically defensible answers," John Rost, chairman of the North American Metal Packaging Alliance, said in a statement.

Vom Saal, however, says Melzer's study rests on a "bedrock" of hundreds of earlier studies that help explain how BPA may contribute to heart disease and diabetes. For example, a study published last month found that BPA suppresses a key hormone that protects the body from heart disease and diabetes.

Taken together, these studies now provide more than enough evidence to err on the side of caution, says John Peterson Myers, a BPA expert who wrote an accompanying editorial. He says the FDA should enact a much stricter safety standard that would reduce the amount of BPA to which Americans could be exposed.

"It's impossible to say that BPA is safe," Myers says.

Melzer's study is based on results from the CDC's 2003-2004 National Health and Nutrition Examination Survey, a massive study that includes interviews as well as the results of urine tests and only recently began including information about BPA exposure. The study allows scientists to look for associations, which give doctors a clue about diseases that appear more often among people exposed to different chemicals.

Authors note that their study — while groundbreaking in many ways — has limitations.

The survey provides just a snapshot of patients, interviewing them one time, Melzer says. A study like this would be more powerful of doctors could follow patients over time to observe whether people with high BPA exposure are more likely to develop diabetes and heart disease.

And because this type of study is designed only to find associations, it doesn't definitively prove that BPA causes disease, Melzer says. That's a common problem in studying environmental toxins. Although scientists can design definitive experiments in animals, it's not ethical to deliberately give a potentially dangerous substance to people, he says.

The American Chemistry Council, which represents companies that make BPA, says it's possible some of the diabetes cases in the study were caused by genetics, rather than environment or lifestyle.

"BPA has been the subject of extensive scientific testing and government reviews worldwide," the council said in a statement. "These reviews have consistently concluded that human exposure levels to BPA are low and within the safe limits set by government authorities."

Yet concern about BPA has grown in the past year, as dozens of scientists have warned that it puts children at risk. Canada has declared BPA to be toxic and has proposed banning it. Lawmakers in the Senate have proposed banning BPA in children's products, while legislators in the House of Representatives have proposed taking it out of food packaging.

Major retailers and manufacturers also are working to take BPA off the shelves.

Wal-Mart and Toys R Us/Babies R Us have announced they are phasing out products that contain BPA. Most baby bottle makers now offer BPA-free alternatives. And PBM Products, which makes store-brand baby formula for Target, Walgreens and other retailers, is working to remove BPA from its metal formula cans.

Myers notes that the amount of lead in children's blood has fallen dramatically in the decades since the USA took lead out of paint and gasoline. "Society has dealt with lead, and our body burdens came down tremendously after we got our political act together," he says.

BPA is so ubiquitous — used in everything from "carbonless" paper receipts to water pipes — that consumers can't shop their way around it, Myer says. The only way to protect vulnerable children, he says, is for industry to stop using the chemical.

"It's mind-boggling," Myers says. "We can't ask moms to be chemical engineers when shopping for their kids, and that is what the current system forces them to be."

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